Radio communication networks were originally developed primarily to provide voice services over circuit-switched networks. The introduction of packet-switched bearers in, for example, the so-called 2.5G and 3G networks enabled network operators to provide data services as well as voice services. Eventually, network architectures will likely evolve toward all Internet Protocol (IP) networks which provide both voice and data services. However, network operators have a substantial investment in existing infrastructures and would, therefore, typically prefer to migrate gradually to all IP network architectures in order to allow them to extract sufficient value from their investment in existing infrastructures. Also to provide the capabilities needed to support next generation radio communication applications, while at the same time using legacy infrastructure, network operators could deploy hybrid networks wherein a next generation radio communication system is overlaid onto an existing circuit-switched or packet-switched network as a first step in the transition to an all IP-based network. Alternatively, a radio communication system can evolve from one generation to the next while still providing backward compatibility for legacy equipment.
One example of such an evolved network is based upon the Universal Mobile Telephone System (UMTS) which is an existing third generation (3G) radio communication system that is evolving into High Speed Packet Access (HSPA) technology. Yet another alternative is the introduction of a new radio access technology, e.g., the so-called Long Term Evolution (LTE) technology. Each new generation, or partial generation, of mobile communication systems provide enhanced performance but typically also add complexity and abilities to mobile communication systems and this can be expected to continue with either enhancements to proposed systems or completely new systems in the future. An example of such added ability is identification of a user's geographical location, aka user geographical location, using proactive assistance data.
The possibility of identifying user geographical location in networks has enabled a large variety of commercial and non-commercial services. Examples of such services are navigation assistance, social networking, location-aware advertising, emergency calls, positioning services etc. Different services may have different positioning accuracy requirements imposed by the application. In addition, some regulatory requirements on the positioning accuracy for basic emergency services exist in some countries, i.e. Federal Communications Commission (FCC) E911 in US.
In many environments, the position of a user or user terminal, also referred to herein as “user equipment” or UE, can be accurately estimated by using positioning methods based on GPS (Global Positioning System). Nowadays networks have also often a possibility to assist UEs in order to improve the terminal receiver sensitivity and GPS start-up performance (Assisted-GPS positioning, or A-GPS). GPS or A-GPS receivers, however, may be not necessarily available in all wireless terminals. Furthermore, GPS is known to often fail in indoor environments and urban canyons. A complementary terrestrial positioning method, called Observed Time Difference of Arrival (OTDOA), has therefore been standardized by Third Generation Partnership Project (3GPP). In addition to OTDOA, the LTE standard also specifies methods, procedures and signaling support for Enhanced Cell ID (E-CID), Advanced Global Navigation Satellite System (A-GNSS) and Uplink-Time Difference Of Arrival (UTDOA).
There are three significant network elements in an LTE positioning architecture, namely a location service (LCS) Client, an LCS target and an LCS Server. The LCS Server is a physical or logical entity managing positioning for the LCS target by collecting measurements and other location information, assisting the user equipment in measurements when necessary, and estimating the LCS target location. The LCS Client is a software and/or hardware entity that interacts with the LCS Server for the purpose of obtaining location information for one or more LCS targets, i.e. the entities being positioned. LCS Clients may reside in the LCS targets themselves. An LCS Client sends a request to LCS Server to obtain location information, and LCS Server processes and serves the received requests and sends the positioning result and optionally a velocity estimate to the LCS Client. A positioning request can be originated from the terminal or the network. A positioning session is initiated by the positioning request and is typically finalized when the positioning result, such as a position given by a set of coordinates, is delivered to the LCS Client.
Position calculation can be conducted, for example, by a positioning server, such as an Enhanced Serving Mobile Location Center (Enhanced SMLC or E-SMLC), a Secure User Plane Location (SUPL) Location Platform (SLP) in LTE or a UE. The former approach corresponds to the UE-assisted positioning mode, whilst the latter corresponds to the UE-based positioning mode. Two positioning protocols operating via the radio network exist in LTE, LTE Positioning Protocol (LPP) and LPP Annex (LPPa). The LPP is a point-to-point protocol between a LCS Server and a LCS target device, used in order to position the target device. LPP can be used both in the user and control plane, and multiple LPP procedures are allowed in series and/or in parallel thereby reducing latency. LPPa is a protocol between evolved-NodeB (eNodeB) and LCS Server specified only for control-plane positioning procedures, although it still can assist user-plane positioning by querying eNodeBs for information and eNodeB measurements. SUPL protocol is used as a transport for LPP in the user plane.
To enable positioning in LTE and facilitate positioning measurements of a proper quality and for a sufficient number of distinct locations, new physical signals dedicated for positioning have been introduced and low-interference positioning subframes have been specified in 3GPP. The new physical signals dedicated for positioning are referred to as positioning reference signals (PRS), although using other physical signals for positioning is not precluded. The PRS are transmitted from one antenna port (R6) according to a pre-defined pattern which is described in the standards document 3GPP TS 36.211. A frequency shift, which is a function of Physical Cell Identity (PCI), can be applied to the specified PRS patterns to generate orthogonal patterns and modeling the effective frequency reuse of six, which makes it possible to significantly reduce neighbor cell interference on the measured PRS and thus improve positioning measurements. Even though PRS have been specifically designed for positioning measurements and in general are characterized by better signal quality than other reference signals, the standard does not mandate using PRS. Other reference signals, e.g. cell-specific reference signals (CRS), could in principle also be used for positioning measurements.
PRS are transmitted in pre-defined positioning subframes grouped by several consecutive subframes (NPRS), i.e. one positioning occasion. Positioning occasions occur periodically with a certain periodicity of N subframes, i.e. the time interval between two closest positioning occasions. The standardized periods N are 160, 320, 640, and 1280 ms, and the number of consecutive subframes may be 1, 2, 4, or 6 as described in 3GPP TS 36.211.
Assistance data is intended to assist a wireless device, such as a user equipment, in its positioning measurements. Hereinafter, assistance data may be referred to as positioning assistance data. Different sets of positioning assistance data is typically used for different positioning methods. The positioning assistance data is typically sent by the positioning server, although it may be sent via other nodes. For example, the positioning assistance data may be sent to an eNodeB for being further sent to the UE, e.g. transparently to eNodeB and also Mobility Management Entity (MME). The assistance data may also be sent by the eNodeB via LPPa to positioning server for further transfer to the UE.
The assistance data may be sent on a request from the wireless device that will perform measurements or in an unsolicited way. In LTE, the assistance data may be provided and requested over the LPP protocol by including provideAssistanceData and requestAssistanceData elements in the LPP message, respectively. The current LTE standard specifies the following structure for provideAssistanceData:
ProvideAssistanceData-r9-IEs ::= SEQUENCE {commonIEsProvideAssistanceDataCommonIEsProvideAssistanceDataOPTIONAL,-- Need ONa-gnss-ProvideAssistanceDataA-GNSS-ProvideAssistanceDataOPTIONAL,-- Need ONotdoa-ProvideAssistanceDataOTDOA-ProvideAssistanceDataOPTIONAL,-- Need ONepdu-Provide-Assistance-DataEPDU-SequenceOPTIONAL,-- Need ON...}
where the commonIEsProvideAssistanceData IE is provided for future extensibility only and not used so far. The LTE assistance data may thus be provided for A-GNSS and OTDOA. The External Protocol Data Unit Sequence (EPDU-Sequence) contains information elements (IEs) that are defined externally to LPP by other organizations, which currently may only be used for Open Mobile Alliance (OMA) LPP extensions (LPPe).
A similar structure exists for requestAssistanceData:
RequestAssistanceData-r9-IEs ::= SEQUENCE {commonIEsRequestAssistanceDataCommonIEsRequestAssistanceDataOPTIONAL,-- Need ONa-gnss-RequestAssistanceDataA-GNSS-RequestAssistanceDataOPTIONAL,-- Need ONotdoa-RequestAssistanceDataOTDOA-RequestAssistanceDataOPTIONAL,-- Need ONepdu-RequestAssistanceDataEPDU-SequenceOPTIONAL,-- Need ON...}where commonIEsRequestAssistanceData may optionally carry the serving cell ID (ECGI).
Since for OTDOA positioning PRS signals from multiple distinct locations need to be measured, the UE receiver may have to deal with PRS that are much weaker than those received from the serving cell. Furthermore, without the approximate knowledge of when the measured signals are expected to arrive in time and what is the exact PRS pattern, the UE would need to do signal search within a large window which would impact the time and accuracy of the measurements as well as the UE complexity. To facilitate UE measurements, the network transmits assistance data to the UE, which includes, among others, reference cell information, neighbor cell list containing PCIs of neighbor cells, the number of consecutive downlink subframes, PRS transmission bandwidth, frequency, etc.
Assistance data delivery is currently not required for UE- or eNodeB-assisted forms of E-CID positioning, but it may be transmitted by using EPDU elements. UE-based E-CID location is not supported in this version of the specification, and the assistance data delivery procedure is not applicable to uplink E-CID positioning.
With OMA, the assistance data are enhanced with the possibility to assist a larger range of positioning methods. E.g. assistance data may also be provided for E-CID or other methods of other Radio Access Technology (RATs), e.g. OTDOA UMTS Terrestrial Radio Access (UTRA) or E-OTD Global System for Mobile Communications (GSM), or other Public Land Mobile Network (PLMN) networks.
A multi-carrier system, herein interchangeably called carrier aggregation (CA), allows the UE to simultaneously receive and/or transmit data over more than one carrier frequency, where each of the carrier frequencies is often referred to as a component carrier (CC). One of the CC is the primary carrier, which is also interchangeably called the anchor carrier or even primary component carrier (PCC). The remaining ones are called the secondary or supplementary carriers or even secondary component carrier (SCC). The cells in the serving sector are called serving cells. More specifically, the serving cells may be a primary serving cell (PCell) and one or more secondary serving cell(s) (SCells). The PCell is on the primary CC (PCC), and SCells are on the secondary CCs (SCCs). The primary carrier carries all common and UE-specific control channels. The secondary carrier may contain only the minimum necessary signaling information and signals, typically cell-specific, e.g. those signals or channels that are UE-specific may be not present in the secondary carrier. The configured primary cells/primary carrier and the set of secondary cells/secondary carriers are typically UE specific, and may also be activated or deactivated. The multi-carrier concept is used in both HSPA and LTE.
The same is true for the uplink primary carriers. For example in a multi-carrier system comprising of 2 DL (F1_DL, F2_DL) and 2 UL carriers (F1_UL, F2_UL), some of the UEs may have F1_DL as the primary carrier and remaining ones may have F2_DL as their primary carrier. The network is able to change the primary carrier of the UE, also referred to as primary carrier switching, at any time. Primary carrier switching is done, for example, to balance the load on different carriers.
In a scenario, where the primary carrier is changed during an ongoing positioning session, a problem may be that performance of the positioning session is degraded in terms of, for example, accuracy and speed.
Another scenario will now be described with reference to a generic telecommunication system. The generic telecommunication system comprises a user equipment, a first and a second cell managed by a radio base station. In other exemplifying scenarios, the first and second cells may be managed by different radio base stations. Firstly, the user equipment is served by the first cell. The user equipment may, as an example, move such that it no longer is within coverage of the first cell. Then, a so called handover from the first cell to the second cell is performed as the user equipment moves into a coverage area of the second cell. In this scenario, a problem may be that when the handover occurs during an ongoing positioning session, performance of the positioning session is degraded in terms of, for example, accuracy and speed.
A high-level positioning architecture, as it is currently standardized in LTE, is illustrated in FIG. 7, where the LCS target is a terminal 120, and the LCS Server is an E-SMLC 102 or an SLP 104. In the figure, the control plane positioning protocols with E-SMLC 102 as the terminating point are shown as the three arrows labeled LCS-AP, LPPa, and LPP, disposed, at least in part, between the E-SMLC 110 and the MME 106, and the user plane positioning protocol is shown by the arrows labeled SUPL/LPP and SUPL. SLP 104 may comprise two components, SPC and SLC, which may also reside in different nodes. In an example implementation, SPC has a proprietary interface with E-SMLC 102, an Llp interface with SLC, and the SLC part of SLP 104 communicates with P-GW (PDN-Gateway) 108 and External LCS Client 119. Also seen in FIG. 7, are the radio access network (RAN) 112 including, e.g., an eNodeB 130. Additional positioning architecture elements may also be deployed to further enhance performance of specific positioning methods. For example, deploying radio beacons 116 and 118 is a cost-efficient solution which may significantly improve positioning performance indoors and also outdoors by allowing more accurate positioning, for example, with proximity location techniques.
To meet LBS demands, the LTE network will deploy a range of complementing methods characterized by different performance in different environments. Depending on where the measurements are conducted and the final position is calculated, the methods can be UE-based, UE-assisted or network-based, each with own advantages. The following methods are available in the LTE standard for both the control plane and the user plane,                Cell ID (CID),        UE-assisted and network-based E-CID, including network-based angle of arrival (AoA),        UE-based and UE-assisted A-GNSS, including A-GPS,        UE-assisted Observed Time Difference of Arrival (OTDOA).Hybrid positioning, fingerprinting positioning and methods using adaptive E-CID (AECID) do not require additional standardization and are therefore also possible with LTE. Furthermore, there may also be UE-based versions of the methods above, e.g. UE-based GNSS, e.g. GPS, or UE-based OTDOA, etc. There may also be some alternative positioning methods such as proximity based location. UTDOA may also be standardized in a later LTE release, since it is currently under discussion in 3GPP. Similar methods, which may have different names, also exist in other RATs, e.g. WCDMA or GSM. Some of these positioning techniques will now be discussed in more detail.        
E-CID positioning exploits the advantage of low-complexity and fast positioning with CID which exploits the network knowledge of geographical areas associated with cell IDs, but enhances positioning further with more measurement types. With Enhanced Cell ID (E-CID), the following sources of position information are involved: the Cell Identification (CID) and the corresponding geographical description of the serving cell, the Timing Advance (TA) of the serving cell, and the CIDs and the corresponding signal measurements of the cells, up to 32 cells in LTE, including the serving cell, as well as AoA measurements. The following UE measurements can be utilized for E-CID in LTE: E-UTRA carrier Received Signal Strength Indicator (RSSI), Reference Signal Received Power (RSRP), Reference Signal Received Quality (RSRQ), and UE Rx-Tx time difference. The E-UTRAN measurements available for E-CID are eNodeB Rx-Tx time difference, also called TA Type 2, TA Type 1 being (eNodeB Rx-Tx time difference)+(UE Rx-Tx time difference), and UL AoA, UE Rx-Tx measurements are typically used for the serving cell, whilst e.g. RSRP and RSRQ as well AoA can be utilized for any cell and can also be conducted on a frequency different from that of the serving cell.
UE E-CID measurements are reported by the UE to the positioning server (e.g. Evolved SMLC, or E-SMLC, or SUPL Location Platform, or SLP, in LTE) over the LTE Positioning Protocol (LPP), and the E-UTRAN E-CID measurements are reported by the eNodeB to the positioning node over the LPP Annex protocol (LPPa). The user equipment may receive assistance data from the network.
The OTDOA positioning method makes use of the measured timing of downlink signals received from multiple eNodeBs at the user equipment. The user equipment measures the timing of the received signals using assistance data received from the LCS server, and the resulting measurements are used to locate the user equipment in relation to the neighboring eNodeBs.
With OTDOA, a terminal measures the timing differences for downlink reference signals received from multiple distinct locations. For each measured neighbor cell, the user equipment measures Reference Signal Time Difference (RSTD) which is the relative timing difference between neighbor cell and the reference cell. The UE position estimate is then found as the intersection of hyperbolas corresponding to the measured RSTDs. At least three measurements from geographically dispersed base stations with a good geometry are needed to solve for two coordinates of the terminal and the receiver clock bias. In order to solve for position, precise knowledge of the transmitter locations and transmit timing offset is needed.
Inter-frequency measurements may in principle be considered for any positioning method, even though currently not all measurements are specified by the standard as intra- and inter-frequency measurements. The examples of inter-frequency measurements currently specified by the standard are Reference Signal Time Difference (RSTD) used for OTDOA, RSRP and RSRQ which may be used e.g. for fingerprinting or E-CID.
The UE performs inter-frequency and inter-RAT measurements in measurement gaps. The measurements may be done for various purposes: mobility, positioning, self organizing network (SON), minimization of drive tests etc. Furthermore the same gap pattern is used for all types of inter-frequency and inter-RAT measurements. Therefore E-UTRAN must provide a single measurement gap pattern with constant gap duration for concurrent monitoring, i.e. cell detection and measurements, of all frequency layers and RATs. The E-UTRA UE supports two configurations comprising of the maximum gap repetition period (MGRP) of 40 and 80 ms; both with the measurement gap length of 6 ms. In practice due to the frequency switching time less than 6 sub-frames but at least 5 full sub-frames are available for measurements within each such measurement gap.
In LTE, measurement gaps are configured by the network to enable measurements on the other LTE frequencies and/or other RATs, e.g. UTRA, GSM, CDMA2000, etc. The gap configuration is signaled to the UE over RRC protocol as part of the measurement configuration. A UE that requires measurement gaps for positioning measurements, e.g., OTDOA, may send an indication to the network, e.g. eNodeB, upon which the network may configure the measurement gaps. Furthermore, the measurement gaps may need to be configured according to a certain rule, e.g. inter-frequency RSTD measurements for OTDOA require that the measurement gaps are configured according to the inter-frequency requirements in 3GPP 36.133, Section 8.1.2.6, e.g. not overlapping with PRS occasions of the serving cell and using gap pattern #0.
In general, in LTE inter-RAT measurements are typically defined similar to inter-frequency measurements, e.g. they may also require configuring measurement gaps like for inter-frequency measurements, but just with more measurements restrictions and often more relaxed requirements for inter-RAT measurements. As a special example, there may also be multiple networks using the overlapping sets of RATs. The examples of inter-RAT measurements specified currently for LTE are UTRA FDD CPICH RSCP, UTRA FDD carrier RSSI, UTRA FDD CPICH Ec/No, GSM carrier RSSI, and CDMA2000 1x RTT Pilot Strength.
For positioning, assuming that LTE FDD and LTE TDD are treated as different RATs, the current standard defines requirements only for FDD-TDD and TDD-FDD inter-frequency measurements, and the requirements are different in the two cases. There are no other inter-RAT measurements specified within any separate RAT for the purpose of positioning and which are possible to report to the positioning node, e.g. E-SMLC in LTE.
Intra-RAT multi-carrier system means that all the component carriers belong to the same RAT e.g. LTE FDD multi-carrier system, LTE TDD multi-carrier system, UTRAN FDD multi-carrier system, UTRAN TDD multi-carrier system and so on.
In LTE multi-carrier system, it is possible to aggregate a different number of component carriers of different bandwidths in the UL and the DL as illustrated in FIGS. 8 and 9.
The component carriers may be contiguous, e.g., as shown in FIG. 8, or non-contiguous, e.g., as shown in FIG. 9. Furthermore in case of non-contiguous carriers, they may belong to the same frequency band or to different frequency bands. A hybrid carrier aggregation scheme comprising of contiguous and non-contiguous component carriers are also envisaged in LTE. The simultaneous transmission and/or reception of the carriers enable the UE to significantly increase its data reception and transmission rates. For instance, 2×20 MHz aggregated carriers in LTE multi-carrier system would theoretically lead to two-fold increase in data rate compared to that attained by a single 20 MHz carrier.
In LTE advanced, several contiguous and non-contiguous carrier aggregation scenarios are being considered. A scenario comprising of 5 contiguous component carriers each of 20 MHz, i.e. 5×20 MHz, is being considered for LTE TDD. Similarly for LTE FDD a scenario comprising of 4 contiguous component carriers each of 20 MHz, i.e. 5×20 MHz, in the downlink and 2 contiguous component carriers in the uplink is being studied.
In inter-RAT multi-carrier system, the component carriers may belong to different RATs. For example, in such systems one CC may belong to LTE FDD and another one to LTE TDD. Yet another example comprises of CCs belonging to UTRAN FDD and E-UTRAN FDD. In such systems one of the RATs may be considered as the main or primary RAT while the remaining ones as the auxiliary RATs.
A number of issues arise when considering how to adapt positioning and the provision of assistance data to systems which employ multi-carrier/carrier aggregation techniques.
LTE uses orthogonal frequency division multiplexing (OFDM) in the downlink and discrete Fourier transform (DFT)-spread OFDM in the uplink. The basic LTE downlink physical resource can thus be seen as a time-frequency grid as illustrated in FIG. 10, where each resource element corresponds to one OFDM subcarrier during one OFDM symbol interval. In the time domain, LTE downlink transmissions are organized into radio frames of 10 ms, each radio frame consisting of ten equally-sized subframes of length Tsubframe=1 ms as shown in FIG. 11.
Furthermore, the resource allocation in LTE is typically described in terms of resource blocks, where a resource block corresponds to one slot, such as 0.5 ms, in the time domain and 12 contiguous subcarriers in the frequency domain. Resource blocks are numbered in the frequency domain, starting with 0 from one end of the system bandwidth. Downlink transmissions are dynamically scheduled, i.e., in each subframe the base station—typically referred to as an eNB in LTE—transmits control information indicating to which terminals and on which resource blocks the data is transmitted during the current downlink subframe. This control signaling is typically transmitted in the first 1, 2, 3 or 4 OFDM symbols in each subframe. A downlink signal with 3 OFDM symbols as the control region is illustrated in FIG. 12.